Grid and filament damper bar assembly



March 31, 1959 J. HART GRID AND FILAMENT DAMPER BAR ASSEMBLY Filed Feb. 17. 1956 INVENTOR. IJHGK Han-r 4 ENE) United States Patent GRID AND FILAMENT DAMPER BAR ASSEMBLY Jack Hart, North Arlington, N.J., assignor to Radio Corporatlon of America, a corporation of Delaware Application February 17, 1956, Serial No. 566,139

2 Claims. (Cl. 313-279) This invention relates to electron tubes and more especially it relates to tubes of the grid-controlled kind.

A principal object of the invention is to provide an improved damper bar arrangement for electron tubes having a grid surrounding a filamentary member, which member is required to be damped against mechanical vibration.

In certain kinds of electron tubes, especially those employing a fine wire filamentary cathode, it has been found advisable to damp the vibrations of the filament. Various devices have been proposed heretofore for that purpose. While the utilization of filament tensioning means solves the problem to a certain extent, it has been found necessary in certain cases to provide a so-called damping bar which engages the filament intermediate its tensioned end supports. Since the filament is surrounded by a wire grid, usually in the form of a fine wire, helically wound around a pair of supports referred to as side rods, it becomes difiicult to fasten the damping bar to a grid side rod without affecting the spacing of the grid turns adjacent the point at which the damper bar is fastened. Since the damper bar in most cases is welded to the side rod, there is also introduced the danger of the welding spark or are migrating to the adjacent grid turns and may even burn or sever them. The present invention has for one of its main objects the provision of a novel grid construction whereby the filament damper bar can be welded to a grid side rod without danger of changing the critical spacing of the adjacent grid turns or laterals as they are sometimes called, and without danger of burning or severing the said laterals at the time the damper bar is being welded to the grid side rod.

It is a feature of the invention to provide a novel conformation to a wire wound grid adjacent to one of the side rod supports thereof, so as to facilitate the fastening or welding of a filament damper bar to the side rod without distorting or destroying the adjacent grid turns.

Another feature relates to an improved method of shaping a wire Wound grid whereby a damper bar or the like can be easily welded to a grid side rod.

A further feature relates to the novel organization, arrangement and relative location and conformation of parts WhlCh cooperate to provide an improved assembly of a filament with a surrounding grid and a filament damper bar carried by the grid and in damping engagement with the filament.

Other features and advantages will appear as the ensuing description progresses.

In the drawing,

Fig. l is a perspective view of a typical known form of wire wound grid and filament damper bar;

Fig. 2 is a sectional view of Fig. 1;

Fig. 3 is a perspective view of a grid and damper bar according to the invention;

Fig. 4 is a. sectional view of Fig. 3 taken along the r 2,880,352 Patented Mar. 31, l95,9

line 3--3 thereof and viewed in the direction of the arrows;

Fig. 5 is a perspective view of a grid turn molding die member according to the invention;

Fig. 6 is an elevational view of a radio tube with part of the enclosing bulb broken away to show the gridfilament and filament damping bar assembly according to the invention.

Refering to Figs. 1 and 2 there is shown one well known assembly of wire wound grid 8 and damper bar 9 wherein the grid 8 comprises a pair of parallel metal side rods 10, 11 around which is helically wound a fine wire 12. Each of the grid turns is permanently fastened, for example by welding, peening or swaging operations, to the side rods 10 and 11. Usually the side rods 10, 11 are of simple circular cross section and in certain kinds of grids the fine wire where it engages each side rod has a substantially greater radius of curvature than the curvature of the side rod. This relation is clearly shown in the cross-sectional view of Fig. 2. It has been proposed heretofore to attach to one of the side rods a filament damper bar consisting of a wire 14 which is welded to the side rod 11, for example, the wire 14 carrying a coating or body of insulation 15 so that when the damper bar engages the filament it is electrically insulated therefrom.

As will be seen from Fig. 2, the grid turns in effect provide a cage around each side rod and in order to weld the damper wire 14 to the side rod 11 for example,

it is necessary to insert a welding tool between the adjacent grid turns. In many cases the spacing of the adjacent grid turns is so small that it is very diflicult to insert a welding tool between the adjacent grid turns to effect the welding of the wire 14 to the side rod without distorting the adjacent grid turns, and in many cases the welding are or spark migrates to these adjacent turns and may burn out either or both of them. It will be seen, therefore, that this problem arises in wound grids of the type described wherein each grid turn constitutes a pair of so-called grid laterals 16, 17, which laterals are supported from the respective side rods ltl-and 11 by the end sections 18, 19 of each grid turn, which end sections extend a substantial distance in opposite directions and substantially transverse to the laterals 16, 17. Therefore, this problem of welding the damper bar occurs with any type of grid regardless of whether the grid periphery is elliptical, as shown in Fig. 2, or square, rectangular or any other shape. Merely for purposes of explanation it will be assumed that the grid is of elliptical shape.

The above difiiculty is overcome in accordance with the present invention by specially shaping each of the grid turns adjacent one of the side rods so that a clear welding space is provided to enable a welding tool to be used without danger of distorting or burning the grid turns. Thus there is shown in Fig. 3 a grid which in general is similar to the grid of Fig. 1 and for that purpose the corresponding parts bear the same designation numerals in Figs. 1 and 3. However, the end section 19 of each grid turn adjacent to the side rod 11 and on one side of that side rod is bent inwardly of the grid, as indicated in Fig. 4 by the numeral 20. This enables any suitable Welding tool 21 to be placed in contact with the wire 14 of the damper bar without danger of the welding tool striking an arc to the adjacent grid turns, and thus eliminating the likelihood of such turns being accidentally severed during the welding of the grid bar to the side rod 11.

The invention is not limited to any particular manner of shaping the grid adjacent the side rod 11, as above described. Preferably, however, there is used interiorly 3, of the grid a suitable die shaping member 22 (Fig. which has a curved face 23 to define the bending of the portion of each grid turn. A suitable external pressure die (not shown) can cooperate with the die member 22 to shape the grid turns adjacent to the side rod 19, as described.

Fig. 6 shows a completed typical radio tube embodying the invention. It will be understood, of course, that the invention is not limited to any particular construction of such radio tube but merely for explanatory purposes the tube may comprise a glass header 24 through which are sealed the various contact prongs 25. The header 24 supports an electric mount consisting for example of the fine wire filament 26 surrounded by the wire wound grid 23 carrying the filament damper bar 9 which is welded to the grid side rod 11. Any suitable anode or plate electrode 27 may surround the grid and the various electrodes may be assembled as a unit to preserve their interelectrode spacing, for example by means of a lower mica disc insulator 28 and an upper mica disc insulator 29. The lower end of the filament 26 can be electrically joined to the corresponding prong and the upper end of the filament can be held under tension by any suitable tensioning spring support means 30 which is electrically connected to another corresponding prong 25. The grid 8 is likewise connected to a further corresponding prong, as is the plate or anode 27. In Fig. 6 the portions of each grid turn adjacent to the side rod 11 are bent inwardly, as described in connection with Figs. 3 and 4, and the damper bar 9 is welded to the side rod 11 as already described.

It will be understood of course that the invention is not limited to the bending inwardly of all the grid turns along one of the side rods. For example only the two grid turns adjacent the damper bar wire 14 may be preformed inwardly for that purpose. In some cases it may be desirable to weld the damper bar wire 14 to both side rods 10 and 11. In that event the grid turns adjacent to the side rod 10 may be preformed inwardly of the grid to provide a clear space for Welding the damper bar wire 14 to the side rod 10.

Various changes and modifications may be made in the disclosed embodiments consonant with the scope of the appended claims.

What is claimed is:

1. The method of making a filament damper bar and grid assembly which comprises winding a fine wire grid around a pair of spaced parallel grid side rods, fastening each turn of the grid to said side rods, die shaping the ends of the grid turns disposed to one side only of a plane including said side rods and adjacent to but one of said side rods to form said ends inwardly of the grid and thereby to form a substantially unobstructed region for welding to said one of said supports, a filament damper bar, inserting said damper bar into the grid between said adjacent turns, and extending a welding tool into said region and welding said damper bar to said one of said side rods.

2. In the art of manufacturing electron tubes of the kind comprising a grid helically wound about a plurality of spaced apart support rods, a filamentary electrode extending through said grid along the axis thereof and a damper bar having an insulating portion in contact with said filamentary electrode and a metallic end-portion secured at one end to one of said side rods, the method of securing said metallic end-portion of said damper bar to said one of said support rods which comprises permanently distorting the turns of the grid which lie adjacent to the region of the support rod to which said damper bar is to be attached to provide a substantially unobstructed welding area for the reception of a Welding tool, bringing said welding tool into said welding area and into electrical contact with said support rod and said end-portion of said damper bar, and applying a welding current to said assembly through said welding tool to weld said damper bar to said support rod.

References Cited in the file of this patent UNITED STATES PATENTS 2,255,906 Umbreit Sept. 16, 1941 2,259,703 Miller Oct. 21, 1941 2,570,606 Simpson Oct. 9, 1951 2,680,208 Gehrke June 1, 1954 FOREIGN PATENTS 651,045 Great Britain Mar. 7, 1951 

